The integration of IPT on data networks (e.g., Internet), made many features available to users of Voice over IP (VoIP) that were not necessarily available to users of traditional telecommunication networks or systems, such as, for example, the Public Switched Telephone Networks (PSTN). One such feature now available by Cisco, as an example, is Cisco's Extension Mobility which, among other things, allows a user to log onto any extension mobility-enabled IP device (e.g., an IP Telephone) with a user's ID credentials and to transfer their user profile to that telephone. The transfer of the user's profile configures the extension mobility-enabled IP telephone as their own, on a temporary basis, with the user's preferences such as line numbers, speed dials, services, permissions, and other user-specific properties. This makes employee desk-sharing and roaming within an organization practical. Although the basic extension mobility feature does not allow users to traverse between different IPT clusters such as in different cities within the network or routed networks, an enhancement to extension mobility is provided allowing users to log onto any enhanced mobility-enabled IP device (e.g., IP Telephone) regardless of the unified communications manager cluster within the overall network. The user may log in with a combination of user credentials (e.g., user ID and PIN, biometric, magnetic and/or smart card) and the user's profile is transferred to that telephone and their directory number is inserted into the local call control agent. The authentication server then instructs the call control agent to provision the enhanced extension mobility-enabled IP telephone as his own on a temporary basis, with the user's preferences such as line numbers, speed dials, services, permissions, and other user-specific properties configured accordingly. This temporary visitor “registration” may be cross-cluster.
In other words, the enhanced extension mobility feature allows users to traverse different clusters (administrative domains) within a network. However, in current VoIP deployments that cover various regions, a dialing plan is generally setup with the local regional PSTN dialing codes. The dial search patterns are stored in a locally significant scope called a partition with each phone line number assigned to a partition. Within the current context, the directory number portability provided by the current feature functionally operates as a “call forward all” wherein all incoming calls are first routed to the user's “home” call control agent (location where their directory number is registered) and thereafter routed to the “guest” telephone where the user is authenticated to use. Although the user's directory number is “portable” in this scheme, it is effectively tied to the user's home call control agent and the user cannot move between administrative domains. This permanent registration of the directory number to a “home” call control agent may cause a single point of failure in a highly mobile environment, as well as sub-optimal routing of voice calls within the network. It does not provide seamless directory number mobility across multiple clusters within one or more enterprise data network domains. It does not associate a user's directory number to the potentially mobile user (analogous to their social security number) but instead registers the user's directory number with the user's home IP device or home unified communications manager cluster and provides re-direction of incoming connection requests from the user's home unified communications manager cluster to the cluster where the user is temporarily “registered” as a visitor. It is to be appreciated that this is not a true registration of the user's DN with the visited cluster, call control agent or temporary device.